The overall objective of this pilot study is to provide effect size estimates and justification, clinical trial and intervention feasibility data, and procedural materials for a full-scale clinical trial that will rigorously test the efficacy and mechanisms of action of the Dietary Approaches to Stop Hypertension (DASH) as adjunct therapy to usual care for adults with not-well-controlled asthma. Asthma is a major public health problem affecting ~300 million people worldwide. The dramatic increase of asthma prevalence in the U.S. and many other westernized countries in recent decades signal a dominant role of the environment in affecting the complex genetics and developmental pathophysiology of this disease. As a hallmark of westernization, rapid changes in diet, including adoption of a more processed and convenience oriented diet, have resulted in a chronic metabolic surplus and a relative reduction in the intake of complex carbohydrates and micronutrients. The available literature on the relationship between diet and asthma has taken a reductionist approach by focusing largely on individual nutrients. However, people do not eat individual nutrients, but rather a combination of foods from various groups that form a dietary pattern. The DASH encompasses foods and nutrients that have shown potential therapeutic benefits in asthma, but no intervention study has tested the efficacy of the whole diet as a treatment for asthma. In this pilot study, we will enroll 90 patients of Kaiser Permanente Northern California in San Francisco who are between the ages of 18 and 70 years and have not-well-controlled asthma. Subjects will be randomly assigned in a 1:1 ratio to the DASH intervention or the usual care control. The DASH intervention will involve 8 group and 3 individual sessions in the initial 14 weeks, followed by 3 monthly phone consultations. Follow-up assessments will occur at 3 and 6 months. The primary aim is to evaluate the potential effect of the DASH diet on a validated composite measure of asthma control, the Juniper Asthma Control Questionnaire. Secondary outcomes include lung function, asthma-specific quality of life, rescue medication use, system-free days, and asthma exacerbations. Additionally, we will explore changes in inflammatory markers (e.g., fractional exhaled nitric oxide) important to asthma pathophysiology and their potential mediating effects on treatment response. We also will conduct exploratory subgroup analyses defined by genotypes (e.g., polymorphisms on glutathione S transferase gene) and phenotypes (e.g., obesity). Furthermore, this pilot study will provide critical feasibility data and procedura materials to optimize patient accrual and retention, intervention acceptance and adherence, eligibility criteria, randomization and blinding procedures, and data collection, processing and analysis plans for the full trial. This research is significant because it aims to test an innovatie approach to improving asthma control among the millions of Americans with this common chronic disease. It meets NHLBI's funding priority for research to increase the evidence base for refining clinical guidelines and public health recommendations regarding dietary and other lifestyle modifications in asthma.